1. Field of the Invention
The present invention relates to a current sensor capable of precisely measuring current which flows through a conductor line.
2. Description of the Related Art
In order to accurately detect small control current flowing in a circuit of a control device, a method of connecting resistors in series in the circuit and measuring a voltage drop in the resistors is used in general. In this case, however, a load different from the control system is given, and there is a possibility that an adverse influence may be exerted on the control system. Consequently, a method of indirectly measuring a control current by detecting the gradient of a current magnetic field produced by the control current has been used. Specifically, an example includes a method of detecting a magnetic flux produced in a center portion of a toroidal core using a Hall device, the magnetic flux being produced by coiling a measurement line around the toroidal core to supply control current to the measurement line.
However, a current sensor capable of realizing the above-described method has problems that a miniaturization is difficult and that the linearity of detection sensitivity or high-frequency response are inadequate, etc. For this reason, a current sensor, in which a giant magnetoresistive element (hereinafter referred to as GMR element) developing a Giant Magneto-Resistive effect is arranged in a current magnetic field produced by the control current in order to detect its gradient, has been proposed (refer to U.S. Pat. No. 5,621,377, for example). Alternatively, in relation to the above, a technique of detecting flaws on a surface of a metal substrate etc. by use of a magnetic sensor provided with a GMR element has been also disclosed. The current sensor using such GMR elements can improve the detection sensitivity and high-frequency response relatively, and what is more, a detection characteristic that is stabilized against a temperature change is obtainable.
Also, although not using GMR elements, a current sensor, which includes a conductor line curved like a U-shape so as to include a pair of parallel portions facing each other and a magneto-sensitive resistor (barber pole structure) disposed on the parallel portions, respectively, has been proposed (for example, refer to Japanese Unexamined Patent Publication No. 6-294854). In the current sensor, current magnetic fields are produced by sending a current to be detected through the U-shaped conductor line, and are detected using the magneto-sensitive resistor. According to this sensor, since current magnetic fields change in proportion to a distance from the center position to the pair of parallel portions of the U-shaped conductor line, the current to be measured of a relatively broad range can be measured precisely and easily by adjusting the disposing position of the magneto-resistive resistor.